1. Field of the Invention
The present invention relates generally to manufacturing RFID tag webstock, and, in particular, to high-speed roll-to-roll manufacture of RFID tag webstock.
2. Description of the Related Art
In general, in the descriptions that follow, we will italicize the first occurrence of each special term of art that should be familiar to those skilled in the art of radio frequency (“RF”) communication systems. In addition, when we first introduce a term that we believe to be new or that we will use in a context that we believe to be new, we will bold the term and provide the definition that we intend to apply to that term. In addition, throughout this description, we will sometimes use the terms assert and negate when referring to the rendering of a signal, signal flag, status bit, or similar apparatus into its logically true or logically false state, respectively, and the term toggle to indicate the logical inversion of a signal from one logical state to the other. Alternatively, we may refer to the mutually exclusive boolean states as logic_0 and logic_1. Of course, as is well known, consistent system operation can be obtained by reversing the logic sense of all such signals, such that signals described herein as logically true become logically false and vice versa. Furthermore, it is of no relevance in such systems which specific voltage levels are selected to represent each of the logic states.
In accordance with our prior invention previously disclosed in the Related References, the amplitude modulated (“AM”) signal broadcast by the reader in an RFID system will be electromagnetically coupled to a conventional antenna, and a portion of the current induced in a tank circuit is extracted by a regulator to provide operating power for all other circuits. Once sufficient stable power is available, the regulator will produce, e.g., a power-on-reset signal to initiate system operation. Thereafter, the method disclosed in the Related References, and the associated apparatus, dynamically varies the capacitance of a variable capacitor component of the tank circuit so as to dynamically shift the fR of the tank circuit to better match the fc of the received RF signal, thus obtaining maximum power transfer in the system.
In accordance with our invention, an RFID tag may be manufactured using roll-to-roll production technology. Several such manufacturing techniques have been disclosed, for example, in the following patent application publications and issued patents (collectively “Manufacturing Examples”), each of which, in its entirety, is expressly incorporated herein by reference:
Eberhardt, et al., “Radio Frequency Identification TAG Having An Article Integrated Antenna”, U.S. Pat. No. 6,107,920, issued 22 Aug. 2000 (“Eberhardt”);
Green, et al., “RFID Label Technique”, U.S. Pat. No. 6,951,596, issued 4 Oct. 2005 (“Green”);
Ferguson, et al., “RFID Device And Method Of Forming”, U.S. Pat. No. 6,940,408, issued 6 Sep. 2005 (“Ferguson”);
Forster, et al., “Low Cost Method Of Producing Radio Frequency Identification TAGS With Straps Without Antenna Patterning”, U.S. Pat. No. 7,158,037, issued 2 Jan. 2007 (“Forster”);
Brod, et al., “Device And Method For Printing A Web”, US 2006 /0230966, published 19 Oct. 2006 (“Brod”);
Lawrence, et al., “Electromagnetic Radiation Decoupler”, US 7,768,400, issued 3 Aug. 2010 (“Lawrence”);
Fox, et al., “RF TAG Application System”, U.S. Pat. No. 6,280,544, issued 28 Aug. 2001 (“Fox”); and
Palmer, et al., “Method Of Forming Labels Containing Transponders”, U.S. Pat. No. 6,019,865, issued 1 Feb. 2000 (“Palmer”).
Typical, prior-art methods of roll-to-roll manufacturing of RFID tags are shown in Green and Brod. Disadvantages of such prior art roll-to-roll manufactured tags include performance which is, at best, severely limited if the tag is attached proximate an interfering substance. By this term, we mean any substance, material, composition of matter, or the like, usually at least partially electrically conductive, that significantly affects the impedance of the tag's antenna. In such applications, tags may be mounted, for example, on a metal surface, on an outside portion of a container of liquid, or, in an extreme example, immersed, in whole or in part, in a container of liquid. Prior art designs, e.g., Lawrence, typically achieve usable on-metal performance by using thicker substrates, sometimes in combination with multiple layers of metal. However, both thick substrates and additional metal layers add substantial cost to tag manufacturing. In addition, the thickness required by prior-art designs has meant that tags had to be produced and handled in singulated form, rather than in long continuous rolls. As a result, such prior-art metal-mount tags have not been adopted in high-volume applications that require high-speed automated processing using roll-form RFID labels. Known efforts to decrease the thickness of the substrate of the final, converted tags using available RFID chips have proven impractical. In general, a metal-mount tag must be tuned properly to operate when the tag's antenna is a given standoff distance from the metal surface to which the tag is mounted (where the standoff distance is determined by the substrate thickness under the antenna plus the thickness of any mounting adhesive). As the standoff distance decreases, the bandwidth of a tag dramatically changes and its center frequency becomes more dependent on the exact standoff distance. As the standoff distance gets below about 1 mm, it becomes economically impractical to attain the tight manufacturing tolerances required to manufacture metal-mount tags. Thus, while some prior-art tags can be tuned to adjust for typical standoff distances, no known prior-art metal-mount tags can be manufactured reliably at standoff distances below about 1 mm. Attempts also have been made to thin the substrate by using various specialized materials; however this typically adds unacceptable cost to the finished product.
In general, the inventions disclosed in the Related References focused primarily on maximizing the total power transferred into the chip by automatically adjusting the input impedance of the transceiver (receiver) to match the impedance of the antenna connected to the impedance of the receiver. The inventions focused on a form and manner that is suitable for selectively varying the input impedance of the receiver circuit to maximize received power, especially during normal system operation. Additionally, in light of the power sensitive nature of RFID systems, those inventions further focused on varying the input impedance with a minimum power loss. We submit that what is needed now is a tag adapted to employ our inventions as disclosed in the Related References to produce thinner, more cost effective RFID tags with improved manufacturing robustness. In particular, it is desirable to produce such thin RFID tags compatible with state-of-the-art roll-to-roll manufacturing technologies. It is further desirable to develop such thin RFID tags to achieve a reliable state-of-the-art read range, even when mounted proximate interfering substances. Additionally, keeping in mind the cost sensitive nature of RFID technology in general, it is desirable to produce such thin RFID tags wherein the manufacturing costs, material costs, and physical dimensions are generally optimized as compared to the prior art.